--- Simon Kilby <skukok@y...> wrote:
> Hi all,
> Ive been set the challenge by one of my fellow Maths
> Ungraduates of cracking a code that I claimed was easy
> to break.
> Basically the Plaintext is put into a 3*3 matrix (P),
> and the Codematrix (C), remains constant and is
> invertable.
> I have three Coded matrices with the same C.
> Any ideas?
> Thanks,
> Simon

From your description, this appears to be the Hill cipher.

http://en.wikipedia.org/wiki/Hill_cipher

You could conceivably brute force the matrix, presuming it takes
entries modulo 26. The key space is equivalent to about 40-41 bits.

As others have mentioned, a crib would make things much easier.

Matt